Hybrid carrier sense multiple access system with collision avoidance for IEEE 802.15.4 to achieve better coexistence with IEEE 802.11

ABSTRACT

A wireless smart utility network (Wi-SUN) device participating in a Wi-SUN network for coexistence with a Wi-Fi HaLow network sharing frequency spectra between the networks is provided. The Wi-SUN device includes a receiver to receive packets of neighbor Wi-SUN devices, a memory configured to store computer executable programs including a hybrid carrier-sense multiple access with collision avoidance (CSMA/CA) control program and Wi-SUN backoff control program, a processor configured to execute the hybrid CSMA/CA control program including instructions that steps of estimating a severity of Wi-Fi Halow interference based on one or combination of the severity metrics, selecting a CSMA/CA mode between predetermined CSMA/CA modes in response to the estimated severity, detecting a channel status based on the hybrid carrier-sense multiple access, wherein if the channel status is not idle, a maximum limited number of times for re-attempting a packet transmission is checked to determine an allowability of re-attempting the packet transmission, and a transmitter to transmit packets according to a determination result of the allowability.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. patent application Ser. No.16/676,676, filed Nov. 7, 2019, which is hereby incorporated in itsentirety by reference.

FIELD OF THE INVENTION

This invention relates generally to a Hybrid Carrier Sense MultipleAccess system, more particularly to the Hybrid Carrier Sense MultipleAccess System with collision avoidance for IEEE 802.15.4 to achievebetter coexistence with IEEE 802.11.

BACKGROUND OF THE INVENTION

5G and Internet of Things (IoT) applications have been emerging. A broadrange of wireless communication standards emerge to cater the diverseapplications. IEEE 802.11 is a set of standard family that can operatein the Sub-1 GHz, 2.4 GHz, 5 GHz, 6 GHz and 60 GHz frequency bands. IEEE802.15.4 is set of standard family that can operate in the Sub-1 GHz,2.4 GHz and 6 GHz frequency bands. As a result, both IEEE 802.11standards and IEEE 802.15.4 standards can operate in the Sub-1 GHz, 2.4GHz and 6 GHz frequency bands. In every frequency band, the spectrumallocation is limited, especially in the Sub-1 GHz frequency band, wherebesides IEEE 802.11 and IEEE 802.15.4, there are other wirelesstechnologies such as LoRa and SigFox. It indicates that the co-locatedwireless networks may be forced to share frequency spectrum. In otherwords, they have to coexist. As a result, the coexistence issue must beaddressed, especially, the existing wireless technologies are developedwith coexistence being not well addressed.

The coexistence can be divided into two categories: homogeneouscoexistence, i.e., coexistence of wireless networks using samecommunication protocol, and heterogeneous coexistence, i.e., coexistenceof wireless networks using different communication protocol, e.g.,coexistence of IEEE 802.11 and IEEE 802.15.4. The carrier sense multipleaccess with collision avoidance (CSMA/CA) mechanism is employed by IEEE802.11 and IEEE 802.15.4 to address homogeneous coexistence. However,heterogeneous coexistence is an issue not well addressed. Some wirelesstechnologies are developed without taking heterogeneous coexistence intoaccount, e.g., IEEE 802.15.4g only considers homogeneous coexistence.Some wireless technologies are developed with heterogeneous coexistencein consideration, but with coexistence criteria set to benefit their owndevices, e.g., IEEE 802.11ah defines higher energy detection thresholdsfor coexistence assessment that can lead lower power IEEE 802.15.4gnetworks being severely interfered.

IEEE 802.15.4g is a standard in IEEE 802.15.4 standard family designedfor wireless smart utility networks (Wi-SUN). As a result, IEEE802.15.4g is also known as Wi-SUN. IEEE 802.15.4g only considershomogeneous coexistence and does not provides heterogeneous coexistencemechanism.

IEEE 802.11ah is a standard in IEEE 802.11 standard family and is alsonamed as Wi-Fi HaLow. IEEE 802.11ah is designed to operate in the Sub-1GHz (S1G) frequency band. IEEE 802.11ah provides heterogeneouscoexistence mechanism. It specifies that an S1G station (STA) usesenergy detection (ED) based clear channel assessment (CCA) with athreshold of −75 dBm per MHz to improve coexistence with other S1Gsystems. If a S1G STA detects energy above that threshold on itschannel, then the mechanisms such as changing operating channel anddeferring transmission might be used to mitigate interference.

Is the heterogeneous coexistence mechanism provided in IEEE 802.11ahsufficient? FIG. 1 shows that data packet delivery rates of theco-located IEEE 802.11ah network and IEEE 802.15.4g network operating inS1G frequency band. In some cases, packet(s) may be referred to asframe(s). Clearly, IEEE 802.15.4g network suffers when network trafficis heavy, but IEEE 802.11ah network always achieves near 100% of packetdelivery rate. Therefore, the heterogeneous coexistence mechanismprovided in IEEE 802.11ah does not work well when network traffic isheavy and further heterogeneous coexistence mechanism for IEEE 802.11ahand IEEE 802.15.4g must be provided.

An easy solution is to have IEEE 802.11ah network and IEEE 802.15.4gnetwork operate on non-overlapping frequency channels. However, suchnon-overlapping frequency channels may not be available due to limitedspectrum allocation, especially in the S1G frequency band. As a result,IEEE 802.11ah network and IEEE 802.15.4g network may be forced to sharefrequency band, i.e., coexist.

Accordingly, it is desirable to provide heterogeneous coexistence methodfor IEEE 802.15.4g network to achieve better coexistence with theco-located IEEE 802.11ah network when they share frequency spectrum withthe objective of improving IEEE 802.15.4g network performance withoutdegrading IEEE 802.11ah network performance.

SUMMARY OF THE INVENTION

Some embodiments of the invention are based on a recognition thatspectrum allocation is limited, especially, in the Sub-1 GHz (SIG)frequency band. Accordingly, the co-located IEEE 802.11ah networks andIEEE 802.15.4g networks may be forced to share frequency spectrum, i.e.,the co-located IEEE 802.11ah networks and IEEE 802.15.4g networks haveto coexist.

Some embodiments of the invention are based on a recognition that IEEE802.15.4g does not provide heterogeneous coexistence mechanism and IEEE802.11ah provided energy detection (ED) based Clear Channel Assessment(CCA) mechanism for heterogeneous coexistence, but the higher EDthreshold specified is in favor of IEEE 802.11ah devices. As a result,the co-located IEEE 802.11ah networks can severely interfere with IEEE802.15.4g networks when they share frequency spectrum due to the factthat the higher ED threshold enables IEEE 802.11ah devices to ignorelower power transmissions of IEEE 802.15.4g devices even if thereceiving energy level of the IEEE 802.15.4g transmissions is highenough for IEEE 802.15.4g devices to decode the data being transmitted.The ignorance can cause transmission of IEEE 802.11ah devices collideswith the ongoing transmission of IEEE 802.15.4g devices.

Some embodiments of the invention are based on a recognition that theco-located IEEE 802.11ah networks can also severely interfere with IEEE802.15.4g networks when they share frequency spectrum due to the fasterCSMA/CA mechanism of IEEE 802.11ah. The faster CSMA/CA mechanism enablesIEEE 802.11ah devices to have immediate channel access without randombackoff or have shorter random backoff time period for more aggressivechannel access, which can interrupt IEEE 802.15.4g transmission processand cause IEEE 802.15.4g transmission failure. Accordingly, coexistencemethod must be provided for IEEE 802.15.4 standard family to achievebetter coexistence with IEEE 802.11 standard family and other wirelesstechnologies.

Some embodiments of the invention provide the hybrid carrier sensemultiple access with collision avoidance (CSMA/CA) for IEEE 802.15.4g,i.e., Wi-SUN, to achieve better coexistence with IEEE 802.11ah, i.e.,Wi-Fi HaLow. The hybrid CSMA/CA enables IEEE 802.15.4g devices to switchbetween two CSMA/CA modes, i.e., Mode-1 CSMA/CA and Mode-2 CSMA/CA. InMode-1 CSMA/CA, conventional IEEE 802.15.4 CSMA/CA procedure isperformed. In Mode-2 CSMA/CA, the immediate channel access enabledCSMA/CA procedure is performed. The Mode-1 CSMA/CA is applied if IEEE802.11ah interference is not severe and the Mode-2 CSMA/CA is applied ifIEEE 802.11ah interference is severe. In other words, Mode-2 CSMA/CAprovides potential for IEEE 802.15.4g devices to have immediate channelaccess in order to compete with more aggressive IEEE 802.11ah devices.

Some embodiments of the invention provide methods for IEEE 802.15.4gdevices to determine the severity of IEEE 802.11ah interference. Morespecifically, the channel access failure rate caused by IEEE 802.11ahtransmission, IEEE 802.11ah channel occupancy probability and thecollision probability caused by IEEE 802.11ah transmission are providedfor IEEE 802.15.4g devices to estimate the severity of IEEE 802.11ahinterference.

Some embodiments of the invention are based on a realization that whenchannel becomes idle, the immediate channel access of multiple IEEE802.15.4g devices can also cause collision among IEEE 802.15.4gtransmissions. Accordingly, an optimal probability is provided for IEEE802.15.4g devices such that within a neighborhood, at most one of IEEE802.15.4g devices performs immediate channel access and the rest of IEEE802.15.4g devices perform random backoff with increased the backoffparameters to avoid colliding with immediate channel accesstransmission.

Some embodiments of the invention provide a method for IEEE 802.15.4gdevices to compute optimal probability of the immediate channel access(ICA) such that an IEEE 802.15.4g device has 1/N probability to performimmediate channel access, where N is the total number of IEEE 802.15.4gdevices within a neighborhood. In some cases, the probability of the ICAmay be determined or changed based on a degree of communicationcongestion α measured by individual nodes or PANCs. This can providegreat advantages when the input traffic of peripheral nodes issufficiently low so that the ICA can be performed more frequently when1/N is small.

Some embodiments of the invention provide a method for an IEEE 802.15.4gdevice to determine the number of IEEE 802.15.4g neighbors within itsneighborhood by monitoring neighbor's packet transmissions.

Some embodiments of the invention enable IEEE 802.15.4g devices toperform Mode-2 CSMA/CA by enabling immediate channel access function orconfiguring backoff parameter values different from default parametervalues used in Mode-1 CSMA/CA.

Some embodiments of the invention enable IEEE 802.15.4 devices toperform Mode-2 backoff by configuring different backoff parameter valuesfrom default parameter values used in Mode-1 backoff.

According to some embodiments of the present invention, a wireless smartutility network (Wi-SUN) device participating in a Wi-SUN network forcoexistence with a Wi-Fi HaLow network sharing frequency spectra betweenthe networks includes a receiver to receive packets of neighbor Wi-SUNdevices; a memory configured to store computer executable programsincluding a hybrid carrier-sense multiple access with collisionavoidance (CSMA/CA) control program and Wi-SUN CSMA/CA control program;a processor configured to execute the hybrid CSMA/CA control programincluding instructions that cause the processor to perform steps ofestimating a severity of Wi-Fi Halow interference based on one orcombination of the severity metrics; selecting a CSMA/CA mode betweenpredetermined CSMA/CA modes in response to the estimated severity;computing an optimal probability for performing an immediate channelaccess or a backoff procedure according to the selected CSMA/CA mode;detecting a channel status based on the hybrid carrier-sense multipleaccess, wherein if the channel status is not idle, a maximum limitednumber of times for re-attempting a packet transmission is checked todetermine an allowability of re-attempting the packet transmission; anda transmitter to transmit packets according to a determination result ofthe allowability.

Further, some embodiments of the present invention are based onrecognition that a non-transitory computer readable recoding mediumstoring thereon computer executable programs including a hybridcarrier-sense multiple access with collision avoidance (CSMA/CA) controlprogram and Wi-SUN CSMA/CA control program for coexistence of a Wi-FiHaLow network and a Wi-SUN network sharing frequency spectra between thenetworks, wherein the executable programs cause a processor to performsteps of estimating a severity of Wi-Fi Halow interference based on aseverity estimation metric; selecting a CSMA/CA mode betweenpredetermined CSMA/CA modes in response to the estimated severity;performing an immediate channel access or a backoff procedure accordingto the selected CSMA/CA mode; and detecting a channel status based onthe hybrid carrier-sense multiple access, wherein if the channel statusis not idle, a maximum limited number of times for re-attempting apacket transmission is checked to determine an allowability ofre-attempting the packet transmission.

It should be noted that although the present disclosure describes onmethods/systems for coexistence of IEEE 802.11ah networks and IEEE802.15.4g networks as examples, the methods/systems according to thepresent invention are not limited to the standards of IEEE 802.11ahnetworks and IEEE 802.15.4g networks. For instance, the methods/systemsdescribed in the present disclosure can be applied to IEEE802.15.4standard family including IEEE 802.15.4w or the communication systemswhich use CSMA/CA and random backoff method.

Furthermore, it should be noted that the methods/systems are not limitedto the Sub-1 GHz radio bands used by IEEE 802.11ah and IEEE 802.15.4g.The methods/systems according to the present invention can be applied toother types of communication systems. For instance, the methods/systemscan be applied to systems using industrial, scientific, and medical(ISM) radio bands, which include different communication systems thatoperate based on different communication protocols usingcommon/overlapped frequency bands and can detect the other communicationsystems by detecting signal levels or sensing carriers.

BRIEF DESCRIPTION OF THE DRAWINGS

The presently disclosed embodiments will be further explained withreference to the attached drawings. The drawings shown are notnecessarily to scale, with emphasis instead generally being placed uponillustrating the principles of the presently disclosed embodiments.

FIG. 1 shows sample data packets receiving rates of the coexisting IEEE802.11ah network and IEEE 802.15.4g network using coexistence controlmechanisms provided in IEEE 802.11ah standard;

FIG. 2A is a schematic diagram of the heterogeneous system consisting ofthe co-located IEEE 802.11ah network and 82.15.4g network, according tosome embodiments of the present invention;

FIG. 2B is a schematic of a structure of an IEEE 802.15.4g deviceparticipating in forming the networks of FIG. 2A, according to someembodiments of the present invention;

FIG. 3 shows the energy level range in which IEEE 802.11ah devicesinterfere with IEEE 802.15.4g devices due to higher energy detectionthreshold of IEEE 802.11ah;

FIG. 4 shows IEEE 802.11ah and IEEE 802.15.4g backoff parameter valuecomparison;

FIG. 5 shows conventional IEEE 802.15.4-2011 carrier sense multipleaccess with collision avoidance (CSMA/CA) method, according embodimentsof the present invention;

FIG. 6 shows hybrid IEEE 802.15.4 carrier sense multiple access withcollision avoidance (CSMA/CA) method, according to embodiments of thepresent invention;

FIGS. 7A and 7B show examples of data packet delivery rates usingconventional IEEE 802.15.4 CSMA/CA method and hybrid IEEE 802.15.4CSMA/CA method in the presence of IEEE 802.11 interference;

FIGS. 8A and 8B illustrate 802.11ah data packets arriving time periodsthat result in IEEE 802.11ah transmission process that can potentiallyinterfere with a given IEEE 802.15.4g transmission;

FIG. 9 shows the block diagram of the Hybrid CSMA/CA mechanism designedfor IEEE 802.15.4g to allow IEEE 802.15.4g devices to re-determine theseverity of IEEE 802.11ah interference during the backoff process,according to some embodiments of the present invention; and

FIGS. 10A-10C illustrate a flowchart of the CSMA-CA algorithm duplicatedfrom the IEEE Std 802.15.4-2015 as a reference.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the present invention are described hereafterwith reference to the figures. It would be noted that the figures arenot drawn to scale elements of similar structures or functions arerepresented by like reference numerals throughout the figures. It shouldbe also noted that the figures are only intended to facilitate thedescription of specific embodiments of the invention. They are notintended as an exhaustive description of the invention or as alimitation on the scope of the invention. In addition, an aspectdescribed in conjunction with a particular embodiment of the inventionis not necessarily limited to that embodiment and can be practiced inany other embodiments of the invention.

IEEE 802.11 standard family and IEEE 802.15.4 standard family are twowidely used wireless technologies for local area networks. IEEE 802.11ahand IEEE 802.15.4g are two standards designed to operate in the Sub-1GHz (S1G) frequency band while IEEE 802.15.4g can also operate in the2.4 GHz frequency band. IEEE 802.11ah and IEEE 802.15.4g are used asexample technologies to embody the coexistence methods of the invention.The technologies provided can be applied to coexistence of IEEE 802.11standard family and IEEE 802.15.4 standard family.

IEEE 802.11ah is also called as Wi-Fi HaLow. An IEEE 802.11ah networktypically consists of an access point (AP) and stations (STAs). IEEE802.11ah AP can associate with more than 8000 STAs. IEEE 802.15.4g isdesigned for wireless smart utility networks (Wi-SUN). Therefore, IEEE802.15.4g is also known as Wi-SUN, and an IEEE 802.15.4g may be referredto as a Wi-SUN device. There are millions of IEEE 802.15.4g devices thathave already been deployed. IEEE 802.15.4g network typically consists ofa personal area network coordinator (PANC) and the associated devicescalled nodes. A PANC can associate with more 60000 nodes. Both IEEE802.11ah and IEEE 802.15.4g are designed for smart utility, smart cityand other IoT applications. As a result, it is highly possible that IEEE802.11ah networks and IEEE 802.15.4g networks are co-located and sharefrequency band, i.e., coexist. Therefore, ensuring harmoniouscoexistence of IEEE 802.11ah network and IEEE 802.15.4g network in theS1G frequency band is critical.

IEEE 802.15.4g does not provides heterogeneous coexistence mechanism.IEEE 802.11ah provides heterogeneous coexistence mechanism. An S1G STAuses energy detection (ED) based clear channel assessment (CCA) with athreshold of −75 dBm per MHz to improve coexistence with other S1Gsystems. If a S1G STA detects energy above that threshold on itschannel, then the mechanisms such as changing operating channel anddeferring transmission might be used to mitigate interference.

There is a question as to if the heterogeneous coexistence mechanism isprovided in IEEE 802.11ah sufficient to coexist well with IEEE 802.15.4gnetwork. FIG. 1 shows that data packet delivery rates of the co-locatedIEEE 802.11ah network and IEEE 802.15.4g network operating in S1Gfrequency band. Clearly, IEEE 802.15.4g network suffers when networktraffic is heavy, but IEEE 802.11ah network always achieves near 100% ofpacket delivery rate. Therefore, the heterogeneous coexistence methodfor IEEE 802.15.4g must be provided to achieve better performance in thepresence of IEEE 802.11ah interference.

FIG. 2A shows a schematic of the heterogeneous system consisting of thecoexisting IEEE 802.11ah network 200 and IEEE 802.15.4g network 205.IEEE 802.11ah network 200 contains an AP 201 and the associated STAs202, in which AP 201 and STAs 202 communicate via the IEEE 802.11ahwireless link 203. IEEE 802.15.4g network 205 contains a PANC 206 andthe associated nodes 207. PANC and nodes communicate through the IEEE802.15.4g wireless link 208. Two networks are co-located close enough sothat portion of the IEEE 802.15.4g network 205 is within thecommunication range of IEEE 802.11ah network 200. Therefore, one networkcan interfere with another network when their operating channels sharefrequency spectrum.

The topology of IEEE 802.11ah network and IEEE 802.15.4g network can bestar, mesh or tree, e.g., IEEE 802.11ah network 200 is star topology andIEEE 802.15.4g network 205 is tree topology. In some cases, a smartmeter system network (IEEE 802.15.4g) can be configured as treetopology. It should be noted that each of the connections of the treetype configurations can be changed according to the states ofcommunications. In other words, each node can be connected by a multipop (Post Office Protocol) manner: it is not necessary for all nodes tobe directly connected to the PANC 206, e.g. PANC 206↔15.4 g Node207↔15.4 g Node 209.

According to embodiments of the present invention, as the interferenceby IEEE 802.11ah wireless networks can be detected by each node of IEEE802.15.4g wireless networks and the use of immediate channel access canbe determined, the present invention can be applied to multiple-cellconfigurations which include plural IEEE 802.15.4g networks.

Furthermore, the whole IEEE 802.15.4g networks can be configured tocollect information related network traffic to detect the degree of theinterference caused by IEEE 802.11ah wireless networks.

According to some embodiments of the present invention, a wireless smartutility network device (Wi-SUN device or IEEE 802.15.4g device)participating in a Wi-SUN network for coexistence with a Wi-Fi HaLow(IEEE 802.11ah) network sharing frequency spectra between the networksincludes a receiver to receive packets of neighbor Wi-SUN devices, amemory configured to store computer executable programs including ahybrid carrier-sense multiple access with collision avoidance (CSMA/CS)control program and Wi-SUN Backoff control program, and a processorconfigured to execute the computer executable programs includinginstructions, where the instructions cause the processor to performsteps of estimating a severity of Wi-Fi Halow interference based on aseverity estimation method, switching (selecting) a CSMA/CA mode betweenpredetermined CSMA/CA modes in response to the estimated severity; andperforming an immediate channel access or a backoff procedure accordingto the selected CSMA/CA mode. Further the Wi-SUN device includes atransmitter to transmit packets according to a result of the steps.

FIG. 2B shows an example of a structure of an IEEE 802.15.4g deviceparticipating in forming the networks of FIG. 2A, in which an IEEE802.15.4g device 210 may include a processor 214, memory 212, a powersource 216, a transceiver 218 including transmitter, receiver and energydetector and a RF antenna 220. Further, control programs are included ina storage 211 in connection with the memory 212, the processor 214 andthe transceiver 218. The control programs 211 include a CSMA/CA modecontrol (program) 224, Mode-1 CSMA/CA program 226 and Mode-2 CSMA/CAprogram 228, and a timer 222 that is used by the transceiver 218 toperform the CSMA/CA mode control (program) 224. Depending on theseverity of IEEE 802.11ah interference, the hybrid CSMA/CA mode controlprogram 224 can either call conventional IEEE 802.15.4 CSMA/CA procedureor immediate channel access enabled CSMA/CA procedure.

The Interference Caused by the Higher Energy Detection (ED) Threshold ofIEEE 802.11Ah

IEEE 802.11ah defines higher ED threshold than the ED threshold of IEEE802.15.4g, which is typically 10 dB greater than the IEEE 802.15.4greceiver sensitivity (RS). If an IEEE 802.15.4g receiver detects theenergy level of IEEE 802.15.4g signal above the receiver sensitivity,the receiver can decode the data from the transmitted signal.

FIG. 3 shows the distribution of IEEE 802.15.4g receiver sensitivity310, IEEE 802.15.4g ED threshold 320 and IEEE 802.11ah ED threshold 330in energy domain. These three parameters divide energy domain into fourregions 340, 350, 360 and 370. The region 340 represents the energylevel range less than IEEE 802.15.4g receiver sensitivity 310, theregion 350 represents the energy level range greater than IEEE 802.15.4greceiver sensitivity 310 but less than IEEE 802.15.4g ED threshold 320,the region 360 represents the energy level range greater than IEEE802.15.4g ED threshold 320 but less than IEEE 802.11ah ED threshold 330.Further, the region 370 represents the energy level range greater thanIEEE 802.11ah ED threshold 330.

The higher ED threshold of IEEE 802.11ah can lead IEEE 802.11ahtransmission colliding with IEEE 802.15.4g transmission. If the detectedenergy level of an IEEE 802.15.4g packet transmission is in region 380,the packet is readable by IEEE 802.15.4g device, but IEEE 802.11ahdevice ignores the detected packet transmission since the detectedenergy level is lower than IEEE 802.11ah ED threshold 330, in otherwords, IEEE 802.11ah device treats channel as idle. In this case, if itsenses channel idle for more than distributed interframe space (DIFS)time period or its backoff counter reaches to zero, IEEE 802.11ah devicewill start transmission that collides with ongoing IEEE 802.15.4g packettransmission.

The Interference Caused by the Faster CSMA/CA Mechanism of IEEE 802.11Ah

FIG. 4 shows comparison of the CSMA/CA parameter values for IEEE802.11ah and IEEE 802.15.4g. The parameters for IEEE 802.11ah are muchsmaller than corresponding parameters for IEEE 802.15.4g. For example,an IEEE 802.15.4g backoff period is much longer than IEEE 802.11ah timeslot. Therefore, IEEE 802.11ah backoff process is much faster than IEEE802.15.4g backoff process, which leads to much more channel accessopportunities for IEEE 802.11ah devices. For example, if an IEEE802.15.4g device senses channel is idle, it then performs receiving modeto transmission mode switching, i.e., RX-to-TX turnaround, which takes1000 μs. During this turnaround time period, an IEEE 802.11ah device canstart its transmission. As a result, IEEE 802.11ah transmission cancollide with IEEE 802.15.4g transmission. Therefore, IEEE 802.11ahinterferes with IEEE 802.15.4g transmission. Both data collision andacknowledgement collision can be caused by faster IEEE 802.11ah CSMA/CAmethod.

Hybrid CSMA/CA for IEEE 802.15.4 to Achieve Better Coexistence with IEEE802.11

IEEE 802.15.4g device and IEEE 802.11ah device cannot communicate witheach other. Therefore, IEEE 802.15.4g devices cannot coordinate withIEEE 802.11ah devices for interference mitigation. However, IEEE802.15.4g devices can change their behaviors to obtain more channelaccess opportunity when they detect severe interference from IEEE802.11ah devices. IEEE 802.15.4g devices can explore the weakness ofIEEE 802.11ah devices to increase their channel access opportunity. Forexample, an IEEE 802.11ah device must perform random backoff processafter the busy channel is detected. For example, for the first backoff,the backoff time can be 780 μs and for the second backoff, the backofftime can be 1612 μs. Before starting the random backoff process, IEEE802.11ah device must wait for DIFS time period, i.e., the minimum idletime for immediate channel access, which is 264 μs for IEEE 802.11ah.This 264 μs waiting time plus random backoff time may give IEEE802.15.4g devices opportunity to start transmission before IEEE 802.11ahdevices if IEEE 802.15.4g devices perform immediate channel access.However, the immediate channel access by multiple IEEE 802.15.4g deviceswithin same neighborhood can also cause collision. Therefore, anintelligent immediate channel access method needs to be provided forIEEE 802.15.4 standard family.

The CSMA/CA is a mechanism used by both IEEE 802.11 and IEEE 802.15.4standard families for homogeneous coexistence. FIG. 5 shows aconventional IEEE 802.15.4 CSMA/CA procedure 500, which also applies toIEEE 802.15.4g. For non-slotted networks, the conventional IEEE 802.15.4CSMA/CA initials 510 number of backoff (NB) to 0 and backoff exponent(BE) to macMinBE. The CSMA/CA then delays 540 random number of backoffperiods with random number drawn uniformly within interval [0,2^(BE)−1], which is called delay window (DW), where BE starts withmacMinBE and increases until to macMaxBE. When random delay completes,CCA operation is performed 550. If channel is idle 555, the backoffsuccess 585 and IEEE 802.15.4 device proceeds to transmit. If channel isnot idle, NB and BE are updated 590. If the maximum number of backoffhas been performed 565, the backoff fails 570. Otherwise, Backoffprocedure continues (goes to the delays 540). For slotted network,CSMA/CA initiates 512 NB to 0 and contention window (CW) to CW₀, whichequals to 1 or 2 depending on country regulation. CSMA/CA initiates BEto macMinBE 525 or min{2, macMinBE} 520 depending on if battery lifeextension is true 515. The CSMA/CA then locates backoff period boundary530 and delays random number of backoff periods 540. When the randomdelay 540 completes, the CSMA/CA performs CCA 545 at backoff periodboundary. If channel is an idle status 555 and CW is decreased by one instep 575. If CW equals to zero in step 580, the operation goes to thebackoff success 585. Otherwise, another CCA operation is performed 545.If channel is not idle status, then NB, CW and BE are updated in step560. If the maximum number of backoff has been performed in step 565,the operation goes to the backoff fails status in step 570. Otherwise,Backoff procedure continues (goes to step 540).

It can be seen that the larger macMinBE and/or macMaxBE increases delaywindow (DW).

It can also be seen that for both slotted and non-slotted network, theconventional IEEE 802.15.4 CSMA/CA performs the random delay first nomatter how long channel has been idle. Using this CSMA/CA mechanism,IEEE 802.15.4 has disadvantage to compete with more aggressive IEEE802.11, which allows immediate channel access. Therefore, conventionalIEEE 802.15.4 CSMA/CA is not suitable for heterogeneous coexistence,especially for coexistence with more aggressive IEEE 802.11 networks.

Some embodiments of the invention provide hybrid CSMA/CA for IEEE802.15.4 standard family including IEEE 802.15.4g to achieve bettercoexistence with IEEE 802.11 standard family including IEEE 802.11ah.The hybrid CSMA/CA allows IEEE 802.15.4 devices to have immediatechannel access capability when IEEE 802.11 interference is severe.Taking into account of possible collision of immediate channel access bymultiple IEEE 802.15.4 devices, hybrid CSMA/CA aims to allows at mostone of IEEE 802.15.4 devices within a neighborhood to perform immediatechannel access, the rest of IEEE 802.15.4 devices within sameneighborhood perform backoff with increased backoff parameters to avoidcollision with transmission of the immediate channel access. Another keydifference between hybrid CSMA/CA and conventional CSMA/CA for IEEE802.15.4 is the contention window (CW) configuration. In conventionalCSMA/CA shown in FIG. 5 , the CW is set to CW₀ 512, where CW₀ can be 1or 2. If CW0=2, an IEEE 802.15.4 device can transmit packet only ifchannel is idle for two consecutive CCA operations. As shown in FIG. 4 ,CCA time for IEEE 802.11ah is at most 40 μs. However, CCA time for IEEE802.15.4g is 128 μs, which is much longer than 40 μs. Therefore, tocompete with IEEE 802.11ah, hybrid CSMA/CA requires only one CCAoperation as shown in 625 of FIG. 6 .

For instance, as seen in FIG. 2B, a wireless smart utility network(Wi-SUN) device (IEEE 802.15.4g device) participating in a Wi-SUNnetwork for coexistence with a Wi-Fi HaLow network sharing frequencyspectra between the networks may include an energy detector 218 todetect energy level of the packet transmissions, a receiver 218 toreceive packets of neighbor Wi-SUN devices, a memory 212 configured tostore computer executable programs 211 including a hybrid carrier-sensemultiple access with collision avoidance (CSMA/CA) control program 224,a timer 222 and Wi-SUN Backoff control Program (not shown), and aprocessor 214 configured to execute the hybrid CSMA/CA control program224 including instructions. The instructions can cause the processor 214to perform steps (procedures) of estimating a severity of Wi-Fi Halowinterference based on a severity estimation method, switching(selecting) a CSMA/CA mode between predetermined CSMA/CA modes inresponse to the estimated severity, and performing an immediate channelaccess or a backoff procedure according to the selected CSMA/CA mode,and a transmitter 218 to transmit packets.

FIG. 6 shows hybrid CSMA/CA (operation program/procedure) for IEEE802.15.4. Instead of delaying for a random number of backoff periods(step 540 in FIG. 5 ), the hybrid CSMA/CA program first determines ifIEEE 802.11 interference is severe (severe state) in step 605. If802.11ah interference is not severe (non-severe state), the Mode-1CSMA/CA 226, i.e., conventional IEEE 802.15.4 CSMA/CA, is performed inprocedure 500. If IEEE 802.11 interference is severe, the Mode-2 CSMA/CA228 is performed in procedure 600. The Mode-2 CSMA/CA 228 first computesin step 610 an optimal probability for immediate channel access. Basedon the optimal probability, Mode-2 CSMA/CA 228 determines in step 615 ifthe immediate channel access is performed or not. If the immediatechannel access is not performed, the Mode-2 CSMA/CA 228 updates one ormultiple base backoff parameters macMinBE, macMaxBE, BackoffPeriod andmacMinBE in step 620. The Mode-2 CSMA/CA 228 then performs the Mode-1CSMA/CA 226 in procedure 500 using updated backoff parameters. If yes,the Mode-2 CSMA/CA 228 initiates 625 NB to 1, CW to 1 and BE to macMinBEFor non-slotted network, the Mode-2 CSMA/CA 228 immediately performs CCAoperation in step 640. For slotted network, the Mode-2 CSMA/CA 228locates backoff period boundary in procedure 635 and then performs CCAin procedure 640 at boundary of backoff period. If CCA returns idlechannel status 645, the immediate channel access is performed, i.e.,802.15.4 starts transmission, in procedure 650. If CCA returns busychannel status at step 645, the Mode-2 CSMA/CA 228 checks if the maximumnumber of backoff has been performed in step 655. If yes, backoff failsas indicated in step 660. If no, Mode-2 CSMA/CA 228 delays random numberof backoff periods in step 665. When random backoff completes, theMode-2 CSMA/CA 228 updates NB and BE 670 and performs CCA 640 again.

For the backoff parameter update 620 in Mode-2 CSMA/CA, it is desirableto increase values of these parameters in order to avoid collision withthe transmission of the device that is performing immediate channelaccess.

FIG. 7A shows the data packet delivery rates for IEEE 802.11ah and IEEE802.15.4g networks using conventional IEEE 802.15.4 CSMA/CA method. Itcan be seen that IEEE 802.11ah achieves near 100% of packet deliveryrate and IEEE 802.15.4g, however, only gets about 89% of packet deliveryrate. FIG. 7(B) shows the data packet delivery rates for IEEE 802.11ahand IEEE 802.15.4g networks using hybrid IEEE 802.15.4 CSMA/CA method.It can be seen that IEEE 802.11ah still achieves near 100% of packetdelivery rate and in this case, IEEE 802.15.4g obtains about 93% ofpacket delivery rate. Therefore, hybrid CSMA/CA improves IEEE 802.15.4gpacket delivery rate by 4% without degrading IEEE 802.11ah networkperformance.

Optimal Probability Computation for Immediate Channel Access in Mode-2CSMA/CA

Using Mode-2 CSMA/CA, an IEEE 802.15.4g device needs to compute 610optimal probabilities for immediate channel access. To compute thisprobability, an IEEE 802.15.4g device needs to know the number of IEEE802.15.4g neighbors. It can determine number of IEEE 802.15.4g neighborsby monitoring neighbor's packet transmission. Assume there are N_(g)IEEE 802.15.4g devices in a neighborhood and each device D_(i) ^(g)(i=1, 2, . . . , N_(g)) has probability p to take immediate channelaccess and probability 1−p to perform random backoff. Let

$X = {\sum\limits_{i = 1}^{N_{g}}X_{i}}$denote binomial random variable B(N_(g), p), where X_(i) is randomvariable representing decision of device D_(i) ^(g). Then P(X=k)=C_(k)^(N) ^(g) p^(k)(1−p)^(N) ^(g) ^(−k) and E[X]=N_(g)p. To avoid collisionamong IEEE 802.15.4g transmissions due to immediate channel access,optimal strategy is that only one IEEE 802.15.4g device performimmediate channel access and rest of IEEE 802.15.4g devices performrandom backoff, i.e., E[X]=1, which gives optimal probabilityp_(o)=1/N_(g).

Even the optimal probability for the immediate channel access (ICA) is1/N_(g), in some cases, the probability of the ICA may be determined orchanged based on a degree of communication congestion α measured byindividual nodes or PANCs. This can provide great advantages when theinput traffic of peripheral nodes is sufficiently low so that the ICAcan be performed more frequently when 1/N_(g) is small.

Methods to Estimate Severity of IEEE 802.11 Interference in Mode-2CSMA/CA

The key of the hybrid CSMA/CA is to determine IEEE 802.11ah interferenceseverity 605, which is used to switch CSMA/CA mode. The following fourmethods are provided for IEEE 802.15.4g devices to estimate IEEE802.11ah interference severity. These four methods define four metricsto estimate IEEE 802.11ah interference severity, i.e., IEEE 802.11ahenergy detection rate, channel access failure rate caused by IEEE802.11ah, channel occupancy probability by IEEE 802.11ah and collisionprobability caused by IEEE 802.11ah.

Method-1: IEEE 802.11Ah Energy Detection (ED) Ratio

Using energy detection mechanism, an IEEE 802.15.4g device can detectsignal energy that is higher than or equal to IEEE 802.15.4g EDthreshold. Let ED_(total) be the total number of times an IEEE 802.15.4gdevice detected energy level that is higher than or equal to IEEE802.15.4g ED threshold within a time period T. Furthermore, usingcarrier sensing mechanism, an IEEE 802.15.4g device can determine if thedetected signal is IEEE 802.15.4g signal. If not, then the detectedsignal is IEEE 802.11ah signal. Let ED_(ah) be the number of times IEEE802.11ah signal detected. Then, IEEE 802.11ah energy detection ratioR_(ed) ^(h) can be defined as

$\begin{matrix}{R_{ed}^{h} = \frac{ED_{ah}}{ED_{total}}} & (1)\end{matrix}$Method-2: Channel Access Failure Rate Caused by IEEE 802.11Ah

Let N_(caf) be the total number of channel access failure observed by anIEEE 802.15.4g device for total N_(tx) transmission attempts. TheN_(caf) can be decomposed into N_(caf)=N^(h) _(caf)+N^(g) _(caf), whereN^(h) _(caf) is number of channel access failure caused by IEEE 802.11ahand N^(g) _(caf) is the number of channel access failure caused by IEEE802.15.4g. An IEEE 802.15.4g device is able to compute N^(g) _(caf) byusing carrier sense mechanism. To guarantee packet header sensing, IEEE802.15.4g device may start carrier sense early, e.g., start channelsense before backoff counter reaches to zero. Therefore, channel accessfailure rate R^(h) _(caf) caused by IEEE 802.11ah can be computed as

$\begin{matrix}{R_{caf}^{h} = {\frac{N_{caf}^{h}}{N_{tx}} = \frac{N_{caf} - N_{caf}^{g}}{N_{tx}}}} & (2)\end{matrix}$Method-3: IEEE 802.11Ah Channel Occupancy Probability

An IEEE 802.15.4g device can estimate the channel busy time T_(b) bycontinuously sensing channel for a time period T. Its transmission timeand reception time are considered as busy time. Its turnaround time isconsidered as idle time. In addition, IEEE 802.15.4g device is able todetermine the busy time T^(g) _(b) consumed by IEEE 802.15.4gtransmissions via carrier sense. Therefore, IEEE 802.11ah channeloccupancy probability P^(h) _(tx) can be estimated as

$\begin{matrix}{P_{tx}^{h} = \frac{T_{b} - T_{b}^{g}}{T}} & (3)\end{matrix}$Method-4: Collision Probability Caused by IEEE 802.11Ah

An IEEE 802.15.4g device cannot distinguish between collision caused byIEEE 802.11ah or IEEE 802.15.4g. Therefore, the probability of the IEEE802.11ah transmission colliding with IEEE 802.15.4g transmission is usedas a metric to estimate the IEEE 802.11ah interference severity. An IEEE802.11ah transmission can collide with an IEEE 802.15.4g transmissiononly if their transmission time periods overlap.

In the IEEE 802 standards, a data transmission is successful only if itstransmission process completes. Therefore, IEEE 802.11ah transmissionprocess interference impact on IEEE 802.15.4g transmission process isconsidered. In the S1G frequency band, Japanese standard ARIB STD T108allows the maximum 10% duty cycle. Therefore, the unsaturated trafficload assumption holds. An IEEE 802.11ah transmission process caninterfere with a given IEEE 802.15.4g transmission only if the IEEE802.11ah data arrives within a potential time period. This time periodlength is used to estimate the collision probability caused by IEEE802.11ah.

IEEE 802.11ah channel access can be divided into 1) immediate access, inwhich if data arrives, channel is idle and idle channel continues formore than DIFS time period, the data is transmitted without backoff and2) deferred access, in which if data arrives, channel is busy, thenbackoff process is invoked and data transmission is deferred. An IEEE802.11ah device ignores IEEE 802.15.4g transmission if the detectedenergy level is below IEEE 802.11ah ED threshold and detects IEEE802.15.4g transmission if the detected energy level is above IEEE802.11ah ED threshold. Therefore, the IEEE 802.11ah interferencescenarios can be classified into following four cases:

-   -   Case-1: IEEE 802.11ah performs immediate channel access and        ignores IEEE 802.15.4g transmission    -   Case-2: IEEE 802.11ah performs delayed channel access and        ignores IEEE 802.15.4g transmission    -   Case-3: IEEE 802.11ah performs immediate channel access and        detects IEEE 802.15.4g transmission    -   Case-4: IEEE 802.11ah performs delayed channel access and        detects IEEE 802.15.4g transmission

Let T_(gd), T_(ga), T_(hd) and T_(ha) be IEEE 802.15.4g datatransmission time, IEEE 802.15.4g ACK transmission time, IEEE 802.11ahdata transmission time and IEEE 802.11ah ACK transmission time,respectively.

For the Case-1, FIG. 8(A) illustrates the length of potential IEEE802.11ah data arriving period 810 that can interfere with the given IEEE802.15.4g transmission 800. The period length is given by T^(ig)_(im)=T₂−T₁=T_(hd)+SIFS+T_(ha)+T_(gd), where T₁ is the earliest dataarriving time that can result in IEEE 802.11ah transmission process 820interfering with given IEEE 802.15.4g transmission 800, T₂ is the latestdata arriving time that can generate IEEE 802.11ah transmission process830 interfering with given IEEE 802.15.4g transmission 800, and SIFSrepresents short interframe space of IEEE 802.11ah. It is obvious thatthe latest interfering IEEE 802.11ah transmission process 830 can takeplace since IEEE 802.11ah device ignores IEEE 802.15.4g transmission800. Is it possible for the earliest interfering IEEE 802.11ahtransmission process 820 to occur without being detected by IEEE802.15.4g device? The answer is yes. IEEE 802.15.4g RX-to-TX turnaroundtime is 1000 μs. IEEE 802.11ah SIFS is 160 μs. There are 840 μs left forIEEE 802.11ah data transmission and ACK transmission. Even with 1 MHzchannel, IEEE 802.11ah PHY rate ranges from 300 kbps to 16 Mbps. Using 3mbps PHY rate, a 100 byte packet only takes 267 μs. The remaining 573 μsis long enough to transmit IEEE 802.11ah ACK.

For the Case-2, FIG. 2(B) depicts the length of potential IEEE 802.11ahdata arriving period 810 that can interfere with the given IEEE802.15.4g transmission 800. In this case, the earliest interfering IEEE802.11ah transmission process 820 performs random backoff with backoffperiod length greater than zero. The latest interfering IEEE 802.11ahtransmission process 830 happens to select a zero random backoff periodlength. The length of potential IEEE 802.11ah data arriving period 810is given by T^(ig) _(df)=T₂−T₁=max{T_(hd), T_(gd)}+T^(h)_(bo)+T_(hd)+SIFS+T_(ha)+T_(gd), where max{T_(hd), T_(gd)} indicatesthat the busy channel can be caused by either IEEE 802.11ah transmissionor another IEEE 802.15.4g transmission and T^(h) _(bo) is the length ofrandom backoff period of IEEE 802.11ah transmission device. T^(h) _(bo)is random variable with a lower bound 0 and an upper bound CW*52 μs withCW_(min)≤CW≤CW_(max).

Combining Case-1 and Case-2, if IEEE 802.11ah device ignores IEEE802.15.4g data transmission, potential IEEE 802.11ah data arriving timeperiod that can interfere with IEEE 802.15.4g data transmission 800 canbe estimated as

$\begin{matrix}\begin{matrix}{T_{itd}^{ig} = {{P_{i}T_{im}^{ig}} + {\left( {1 - P_{i}} \right)T_{df}^{ig}}}} \\{= {T_{hd} + {SIFS} + T_{ha} + T_{gd} + \left( {1 - P_{i}} \right)}} \\{\left( {{\max\left\{ {T_{hd},T_{gd}} \right\}} + T_{bo}^{h}} \right),}\end{matrix} & (4)\end{matrix}$where P_(i) is the channel idle probability and can be estimated usingmethod later.

Assume IEEE 802.11ah devices have Poisson data arriving distributionwith mean arriving rate λ and the IEEE 802.15.4g transmission device hasN_(h) IEEE 802.11ah neighbors. In a time period T, the probability anIEEE 802.11ah neighbor has no data arriving is

e^(−λT) and the probability all IEEE 802.11ah neighbors have no dataarriving is e^(−NhλT). Therefore, the probability at least one IEEE802.11ah neighbor having data arriving is 1−e^(−NhλT). Thus, theprobability IEEE 802.11ah transmission colliding with the given

IEEE 802.15.4g data transmission is given byp _(cd) ^(ig)=1−e ^(−λN) ^(h) ^(T) ^(icd) ^(ig)   (5)

Case-3 is similar as Case-1, but in this case, the latest interferingIEEE 802.11ah transmission process 830 cannot start at the end of IEEE802.15.4g transmission since during IEEE 802.15.4g transmission 800,channel is considered as busy. Therefore, the latest interfering IEEE802.11ah transmission process 830 can only start at the start of IEEE802.15.4g transmission. As a result, the length of potential interferingIEEE 802.11ah data arriving time period 810 is T^(dt)_(im)=T_(hd)+SIFS+T_(ha).

Similarly, for Case-4, the length of potential interfering IEEE 802.11ahdata arriving time period 810 is given by T^(dt) _(df)=max{T_(hd),T_(gd)}+T^(h) _(bo)+T_(hd) SIFS+T_(ha).

Combining Case-3 and Case-4, if IEEE 802.11ah device detects IEEE802.15.4g data transmission, the potential IEEE 802.11ah data arrivingtime period that can interfere with IEEE 802.15.4g data transmission canbe estimated as

$\begin{matrix}\begin{matrix}{T_{itd}^{dt} = {{P_{i}T_{im}^{dt}} + {\left( {1 - P_{i}} \right)T_{df}^{dt}}}} \\{= {T_{hd} + {SIFS} + T_{ha} + {\left( {1 - P_{i}} \right)\left( {{\max\left\{ {T_{hd},T_{gd}} \right\}} + T_{bo}^{h}} \right)}}}\end{matrix} & (6)\end{matrix}$

The probability IEEE 802.11ah transmission colliding with the given IEEE802.15.4g data transmission is given byp _(cd) ^(dt)=1−e ^(−λN) ^(h) ^(T) ^(itd) ^(dt)   (7)

Notice that P^(dt) _(cd)<p^(ig) _(cd) since T^(dt) _(itd)<T^(ig) _(itd),which is reasonable because if IEEE 802.11ah detects IEEE 802.15.4gtransmission, it takes action to avoid interference.

Besides interfering with IEEE 802.15.4g data transmission, IEEE 802.11ahtransmission can also interfere with IEEE 802.15.4g ACK transmission.IEEE 802.15.4g ACK transmission waiting time AIFS is 1000 μs, which ismuch longer than IEEE 802.11ah DIFS time of 264 μs. Therefore, IEEE802.11ah devices can start transmission process in between IEEE802.15.4g data and IEEE 802.15.4g ACK. The IEEE 802.11ah transmissionprocess can interfere with IEEE 802.15.4g ACK transmission.

Consider that IEEE 802.15.4g ACK is transmitted only if IEEE 802.15.4gdata transmission is successful, the probability of IEEE 802.15.4g ACKtransmission is 1−P^(g) _(c), where P^(g) _(c) is the IEEE 802.15.4gcollision probability caused by both IEEE 802.11ah transmission and IEEE802.15.4g transmission. IEEE 802.15.4g device can compute P^(g) _(c)using number of transmission attempts and number of ACK received.

The probability of the IEEE 802.11ah transmission colliding with theIEEE 802.15.4g ACK transmission can be similarly computed as for theIEEE 802.15.4g data transmission. In this case, however, the busychannel is caused by IEEE 802.15.4g data transmission. If IEEE 802.11ahdevice ignores IEEE 802.15.4g ACK transmission, the probability IEEE802.11ah transmission colliding with the IEEE 802.15.4g ACK transmissionis given byp _(ca) ^(ig)=(1−P _(c) ^(g))(1−e ^(−λN) ^(h) ^(T) ^(ita) ^(ig)   (8)where T ^(ig) _(ita) =T _(hd)+SIFS+T _(ha) +T _(ga)+(1−P _(i))(T _(gd)+T ^(h) _(bo)).

If IEEE 802.11ah device detects IEEE 802.15.4g ACK transmission, theprobability IEEE 802.11ah transmission colliding with the IEEE 802.15.4gACK transmission is given byp _(ca) ^(dt)=(1−P _(c) ^(g))(1−e ^(−λN) ^(h) ^(T) ^(ita) ^(dt)   (9)where T ^(dt) _(ita) =T _(hd)+SIFS+T _(ha)+(1−P _(i))(T _(gd) +T ^(h)_(bo)).

It can also be seen that d^(dt) _(ca)<p^(ig) _(ca) since T^(dt)_(ita)<T^(ig) _(ita).

Finally, combining all cases, the probability of the IEEE 802.11ahtransmission process colliding with the given IEEE 802.15.4gtransmission process P^(h) _(cg) is given by

$\begin{matrix}{P_{cg}^{h} = \left\{ \begin{matrix}{{P_{cd}^{ig} + P_{ca}^{ig}},} & {{if}{IEEE}802.15\text{.4}g{data}{and}{ACK}{ignored}} \\{{P_{cd}^{dt} + P_{ca}^{ig}},} & {{if}{only}{IEEE}802.15\text{.4}g{data}{detected}} \\{{P_{cd}^{ig} + P_{ca}^{dt}},} & {{if}{only}{IEEE}802.15\text{.4}g{ACK}{detected}} \\{{P_{cd}^{dt} + P_{ca}^{dt}},} & {{if}{IEEE}802.15\text{.4}g{data}{and}{ACK}{detected}}\end{matrix} \right.} & (10)\end{matrix}$

The P^(h) _(tx) estimation procedure can be used to estimate P_(i) as

$\begin{matrix}{P_{i} = \frac{T - T_{b}}{T}} & (11)\end{matrix}$

In addition, if IEEE 802.15.4g devices have Poisson data arrivingdistribution with mean arriving rate β. The P_(i) can also be given byP _(i)=(1−β((1+α_(g))T _(gd) +T _(ga)))^(N) ^(g) (1−λ((1−α_(h))T _(hd)+T _(ha)))^(N) ^(h)   (12)where α_(g) and α_(h) are average number of IEEE 802.15.4gretransmission and average number of IEEE 802.11ah retransmission,respectively.

For other 802.11ah traffic patterns such as uniform data arriving, thecollision probability P_(cg) ^(h) can be estimated similarly.

Second Embodiment

Further, according to another embodiment of the present invention, thehybrid carrier sense multiple access with collision avoidance (HybridCSMA/CA) methods described above can be applied to Next-Generation SmartMeters while a transition period from the current generation SmartMeters to the Next Generation Smart Meters, where Smart Meter Systems ofthe current and next generations are operated based on IEEE 802.15.4gand coexist with other wireless systems such as Wi-Fi HaLow (IEEE802.11ah), LoRa and SigFox. In other words, the Hybrid CSMA/CA methodprovides a solution that solves mutual interferences betweenheterogeneous wireless network systems.

FIG. 9 shows an example of the block diagram illustrating the operationsbased on a Hybrid CSMA/CA system designed for IEEE 802.15.4g (beingoperated by Hybrid CSMA/CA algorithm) according to some embodiments ofthe present invention.

Besides the immediate channel access functions, the Hybrid CSMA/CAalgorithm in the second embodiment allows IEEE 802.15.4g devices tore-determine the severity of IEEE 802.11ah interference during thebackoff process according to some embodiments of the present invention.

The block diagram illustrates the flowchart of operations performed byan IEEE 802.15.4g device that performs the operations of the HybridCSMA/CA mechanism. When an IEEE 802.15.4g device is about to transmitpacket(s) (or frame(s)) in response to a transmission request (or atrigger) from the higher layer, the IEEE 802.15.4g device moves to thestart of the Hybrid CSMA/CA at step S1. At step S2, the initializationof sending/transmitting packet is performed. In this case, the IEEE802.15.4g device sets initial parameters for the Hybrid CSMA/CAalgorithm. In some cases, each of the packets may be identified based onsequential numbers and the packets are processed (handled) according tothe sequential numbers.

After the initialization, the operation moves to step S3 a to detect theseverity of the interference from IEEE 802.11ah systems operating in thesame or shared frequency band. Further, it should be noted that theHybrid CSMA/CA method according to the present invention can be appliedto other heterogeneous wireless systems, like SigFox (a French globalnetwork operator f), LoRa (Long Range: a non-cellular long range and lowpower wireless technology), or LPWA (Long Range Wide Area Network). Whenthe IEEE 802.15.4g device detects interference from IEEE 802.11ahdevices and the detected interference level is higher than thepredetermined interference threshold, the IEEE 802.15.4g device movesthe operation to step S3 b. On the other hand, when the Hybrid CSMA/CAalgorithm determines that IEEE 802.11ah devices do not exist in theneighborhood, or the Hybrid CSMA/CA algorithm determines that devicesother than IEEE 802.15.4g devices do not exist in the neighborhood, theoperation moves to step S4 a to perform the standard CSMA/CA algorithm.For instance, when no interference from IEEE 802.11ah devices isdetected or the detected interference level is lower than apredetermined threshold (level), the IEEE 802.15.4g device selectsStandard 802.15.4g CSMA/CA as step S4 a, where the algorithm (oroperations) of step S4 a is illustrated in FIGS. 10A-10C, whichillustrate a flowchart of the standard CSMA/CA algorithm duplicated fromthe CSMA/CA algorithm of FIG. 6-5 in IEEE Std 802.15.4-2015 for thereference of step S4 a.

Step S3 b computes an optimal immediate channel access probability. Inthis case, the IEEE 802.15.4g device computes/counts a number of otherIEEE 802.15.4g devices in the neighborhood to optimize the channelaccess. As described earlier in section of optimal probabilitycomputation for immediate channel access in Mode-2 CSMA/CA, in order toavoid collision among IEEE 802.15.4g transmissions due to immediatechannel access, an optimal strategy is performed such that only one IEEE802.15.4g device performs the immediate channel access and the rest ofIEEE 802.15.4g devices perform random backoff, i.e., E[X]=1, which givesoptimal probability P_(o)=1/N_(g).

Although the Hybrid CSMA/CA algorithm allows IEEE 802.15.4g device toperform the Immediate Channel Access when the device detects severeinterference from IEEE 802.11ah device(s), the immediate channel accesscan cause collision if all IEEE 802.15.4g devices in the neighborhoodattempt to access channel at the same time. In order to avoid suchcollisions, when detecting severe interference from IEEE 802.11ahdevice(s) (S3 a=yes), the Hybrid CSMA/CA algorithm computes the optimalimmediate channel access probability p_(o). Based on the optimalprobability, the Hybrid CSMA/CA algorithm determines if the immediatechannel access is performed at step S3 c. To do so, the Hybrid CSMA/CAalgorithm selects a random value from interval [0, 1]. If the selectedrandom value is less than P_(o) (S3 c=yes), the IEEE 802.15.4g deviceperforms immediate channel access. Otherwise (S3 c=no), the IEEE802.15.4g device does not perform immediate channel access andtherefore, moves to step S4 a. Based on the probability, only one of theIEEE 802.15.4g devices in a neighborhood should perform the ImmediateChannel Access. The rest of the IEEE 802.15.4g devices move to step S4a. The IEEE 802.15.4g device that determines to perform the ImmediateChannel Access (S3 c=yes) configures the parameters with respect to theImmediate Channel Access (Immediate Channel Access parameters).

In specific, step S3 c determines whether the IEEE 802.15.4g deviceshould start immediate channel access or not based on the optimalprobability computed in S3 b. If the IEEE 802.15.4g device decides tonot perform the immediate channel access (S3 c=No), the IEEE 802.15.4gdevice moves to step S4 a, otherwise the IEEE 802.15.4g device moves tostep S3 d. In the cases above, the functions of S3 b and S3 c maximizethe IEEE 802.15.4g transmission probability by considering IEEE802.15.4g internal collision avoidance. In step S3 d, the IEEE 802.15.4gdevice sets the immediate channel parameter(s) and starts the immediatechannel access process.

Step S3 e checks the IEEE 802.15.4g channel access mode, i.e., beaconenabled or non-beacon enabled.

The steps of S3 e/S3 g/S3 h/S3 i perform the standard operationsillustrated in FIG. 6-5 in IEEE Std 802.15.4-2015. When the CSMA/CAalgorithm moves to step “Success”, the IEEE 802.15.4 device is allowedto start transmission. Otherwise, if the CSMA/CA algorithm ends at“Failure”, the IEEE 802.15.4 transmission attempt terminates with achannel access failure.

Part of the descriptions regarding to FIG. 6-5 in IEEE 802.15.4-2015describe the operations as follows.

“FIG. 6-5 illustrates the steps of the CSMA/CA algorithm. If thealgorithm ends in “Success”, the MAC is allowed to begin transmission ofthe frame. Otherwise, the algorithm terminates with a channel accessfailure.

In a slotted CSMA/CA system with the BLE field set to zero, the MACsublayer shall ensure that, after the random backoff, the remainingCSMA-CA operations can be undertaken and the entire transaction can betransmitted before the end of the CAP. If the number of backoff periodsis greater than the remaining number of backoff periods in the CAP, theMAC sublayer shall pause the ackoff countdown at the end of the CAP andresume it at the start of the CAP in the next superframe. If the numberof backoff periods is less than or equal to the remaining number ofbackoff periods in the CAP, the MAC sublayer shall apply its backoffdelay and then evaluate whether it can proceed. The MAC sublayer shallproceed if the remaining CSMA-CA algorithm steps, i.e., two CCAanalyses, or a single continuous CCA analysis of at least PHY CCADuration for the regulatory domains that require listen before talk(LBT) such as the 920 MHz band in Japan, as described in “Applicationsof IEEE Std 802.15.4” [B3], the frame transmission, and anyacknowledgment can be completed before the end of the CAP. If the MACsublayer can proceed, it shall request that the PHY perform the CCA inthe current superframe. If the MAC sublayer cannot proceed, it shallwait until the start of the CAP in the next superframe and apply afurther random backoff delay before evaluating whether it can proceedagain.

In a slotted CSMA-CA system with the BLE field set to one, the MACsublayer shall ensure that, after the random backoff, the remainingCSMA-CA operations can be undertaken and the entire transaction can betransmitted before the end of the CAP. The backoff countdown shall onlyoccur during the first macBattLifeExt Periods full backoff periods afterthe end of the IFS period following the beacon. The MAC sublayer shallproceed if the remaining CSMA-CA algorithm steps, i.e., two CCAanalyses, or a single continuous CCA analysis of at least PHY CCADuration for the regulatory domains that require listen LBT, the frametransmission, and any acknowledgment can be completed before the end ofthe CAP, and the frame transmission will start in one of the firstmacBattLifeExtPeriods full backoff periods after the IFS periodfollowing the beacon. If the MAC sublayer can proceed, it shall requestthat the PHY perform the CCA in the current superframe. If the MACsublayer cannot proceed, it shall wait until the start of the CAP in thenext superframe and apply a further random backoff delay beforeevaluating whether it can proceed again.”

Some embodiments of the present invention add a judgement in thealgorithm at step S3 h. When “Channel idle=No” in step S3 h, theoperation moves to step S3 k. In this case, the function is related to amaximum allowed number of times (threshold) for re-attempting a packettransmission. Further, step S3 k determines if the number of backoffs(NB) exceeds the predetermined macMaxCSMABackoffs. If the result at stepS3 k is “Yes”, the CSMA/CA algorithm moves to step S3 l “Failure” andtherefore, the IEEE 802.15.4g gives up transmission. In other words,when the result in step S3 k indicates that the number of re-attemptedpacket transmission is greater than the maximum allowed number of times,the 802.15.4g device discards the packet (or frame) in step S3 l. If theresult at step S3 k is “No”, the number of re-attempted packettransmission is less than or equal to the maximum allowed number oftimes and therefore, the CSMA/CA algorithm moves to step S3 k-a toperform random backoff.

After finishing backoff, the CSMA/CA algorithm moves to Step S3 j, whichincrements the NB by 1, is an operation that is configured to allow theIEEE 802.15.4g device to re-attempt the packet transmission. Therefore,the CSMA/CA algorithm moves to the initial stage to perform transmissionre-attempting. As a result, IEEE 802.11ah interference severity isre-assessed at step S3 a, which is necessary because wirelessinterference is a dynamic phenomenon.

It is noted, however, the backoff step S3 k-a can be skipped for some802.15.4g packet transmission. For example, if the packet of an802.15.4g device is time critical, the CSMA/CA algorithm can skip stepS3 k-a to reduce delay time. According to some embodiments of thepresent invention, the CSMA/CA algorithm may move to step 3 j byskipping step S3 k-a.

If “Channel idle=yes” at step S3 h, the CSMA-CA algorithm advances tostep S3 i “Success” and the IEEE 802.15.4g device starts packettransmission.

“Channel idle=No” in step S3 h indicates that the IEEE 802.15.4g devicecannot transmit the packet due to the busy channel although device hasattempted to transmit the packet, because a packet transmission is inthe middle of being performed by an IEEE 802.11ah device or another IEEE802.15.4g device.

When the number of re-attempted packet transmission is equal to or lessthan the maximum allowed number of times, the CSMA/CA algorithm returnsto step S3 a, which allows the 802.15.4g device to return to thesequence of steps to re-attempt a packet transmission.

When the CSMA/CA algorithm ends at step S3 l “Failure”, the packet isdiscarded. If a packet to be transmitted is discarded, part of data inthe packet may not be delivered to the destination. In such a case, theupper layer (IP layer or application program) is configured to performre-attempting a packet transmission.

Accordingly, the CSMA/CA algorithms based on some embodiments of thepresent invention can improve Packet Delivery Rate performance of IEEE802.15.4g network by allowing IEEE 802.15.4g devices for more aggressivechannel access and re-detecting the severity of the IEEE 802.11ahinterference during the backoff process.

The above-described embodiments of the present invention can beimplemented in any of numerous ways. For example, the embodiments may beimplemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computer or distributed among multiple computers. Such processorsmay be implemented as integrated circuits, with one or more processorsin an integrated circuit component. Though, a processor may beimplemented using circuitry in any suitable format.

Also, the embodiments of the invention may be embodied as a method, ofwhich an example has been provided. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

Use of ordinal terms such as “first,” “second,” in the claims to modifya claim element does not by itself connote any priority, precedence, ororder of one claim element over another or the temporal order in whichacts of a method are performed, but are used merely as labels todistinguish one claim element having a certain name from another elementhaving a same name (but for use of the ordinal term) to distinguish theclaim elements.

Although the invention has been described by way of examples ofpreferred embodiments, it is to be understood that various otheradaptations and modifications can be made within the spirit and scope ofthe invention.

Therefore, it is the object of the appended claims to cover all suchvariations and modifications as come within the true spirit and scope ofthe invention.

We claim:
 1. A wireless smart utility network (Wi-SUN) deviceparticipating in a Wi-SUN network for coexistence with a Wi-Fi HaLownetwork sharing frequency spectra between the networks, comprising: areceiver to receive packets of neighbor Wi-SUN devices; a memoryconfigured to store computer-executable programs including a hybridcarrier-sense multiple access with collision avoidance (CSMA/CA) controlprogram and Wi-SUN backoff control program; a processor configured toexecute the hybrid CSMA/CA control program including instructions thatcause the processor to perform steps of: estimating a severity of Wi-FiHalow interference based on one or combination of severity metrics;selecting a CSMA/CA mode between predetermined CSMA/CA modes in responseto the estimated severity, wherein a CSMA/CA mode switching selectsMode-1 when the estimated Wi-Fi HaLow interference severity is anon-severe state, wherein the switching selects Mode-2 when theestimated Wi-Fi HaLow interference severity is a severe state, whereinthe instructions further include computing, when Mode-2 is selected, anoptimal immediate channel access probability based on a number ofneighboring Wi-SUN devices monitored by the computing Wi-SUN device,wherein the monitoring is performed by monitoring Wi-SUN neighbor'spacket transmission; computing an optimal probability for performing animmediate channel access or a backoff procedure according to theselected CSMA/CA mode; detecting a channel status based on the hybridcarrier-sense multiple access, wherein if the channel status is notidle, a maximum allowed number of times for re-attempting a packettransmission is checked to determine an allowability of re-attemptingthe packet transmission wherein when a number of backoffs is less thanthe maximum allowed number of times, the number of backoffs isincremented; and a transmitter to transmit packets according to adetermination result of the allowability.
 2. The Wi-SUN device of claim1, wherein the Wi-Fi HaLow interference severity is estimated based onat least one of the severity estimation metrics, an Wi-Fi HaLow energydetection ratio (Red^(h)), a channel access failure rate caused by Wi-FiHaLow (Reaf^(h)), a channel occupancy probability by Wi-Fi HaLow(Ptx^(h) and a collision probability caused by Wi-Fi HaLow (Pcg^(h)). 3.The Wi-SUN device of claim 2, wherein the Wi-Fi HaLow energy detectionratio is computed according to $\begin{matrix}{{R_{ed}^{h} = \frac{ED_{ah}}{ED_{total}}}.} & \end{matrix}$
 4. The Wi-SUN device of claim 2, wherein the channelaccess failure rate caused by Wi-Fi HaLow is computed according to$\begin{matrix}{R_{caf}^{h} = {\frac{N_{caf}^{h}}{N_{tx}} = {\frac{N_{caf} - N_{caf}^{g}}{N_{tx}}.}}} & \end{matrix}$
 5. The Wi-SUN device of claim 2, wherein the Wi-Fi HaLowchannel occupancy probability is computed according to $\begin{matrix}{{P_{tx}^{h} = \frac{T_{b} - T_{b}^{g}}{T}}.} & \end{matrix}$
 6. The Wi-SUN device of claim 2, wherein the collisionprobability caused by Wi-Fi HaLow is computed according to$\begin{matrix}{P_{cg}^{h} = \left\{ {\begin{matrix}{{P_{cd}^{ig} + P_{ca}^{ig}},} & {{if}{IEEE}802.15\text{.4}g{data}{and}{ACK}{ignored}} \\{{P_{cd}^{dt} + P_{ca}^{ig}},} & {{if}{only}{IEEE}802.15\text{.4}g{data}{detected}} \\{{P_{cd}^{ig} + P_{ca}^{dt}},} & {{if}{only}{IEEE}802.15\text{.4}g{ACK}{detected}} \\{{P_{cd}^{dt} + P_{ca}^{dt}},} & {{if}{IEEE}802.15\text{.4}g{data}{and}{ACK}{detected}}\end{matrix}.} \right.} & (10)\end{matrix}$
 7. The Wi-SUN device of claim 1, wherein the predeterminedCSMA/CA modes are Mode-1 and Mode-2, wherein Mode-1 is a standard Wi-SUNCSMA/CA procedure and Mode-2 is an immediate channel access enabledCSMA/CA procedure.
 8. The Wi-SUN device of claim 7, wherein backoffparameter values of Mode-2 CSMA/CA are different from default backoffparameter values of Mode-1 CSMA/CA.
 9. The Wi-SUN device of claim 8,wherein when other Wi-SUN devices are in a neighborhood area, at mostone of the Wi-SUN devices is allowed to perform an immediate channelaccess and a rest of Wi-SUN devices perform backoff by increasing thebackoff parameter values.
 10. The Wi-SUN device of claim 9, wherein thelarger backoff parameters cause a lon ger delay window (LDW), whereinfor each re-backoff, the LDW is determined as: LDW=2*Current LDW. 11.The Wi-SUN device of claim 1, wherein the transmitter transmits thepackets when the computed probability indicates that the immediatechannel access is allowed and the channel is in idle state.
 12. TheWi-SUN device of claim 11, wherein ongoing Wi-SUN transmission processincludes CCA operation→CCA to TX Turnaround→TX start and data TX→Waitingfor ACK→ACK RX.
 13. The Wi-SUN device of claim 12, wherein the Wi-SUNdevice does not sense a channel status again after CCA to TX Turnaround,wherein a Wi-SUN recipient device does not sense the channel from theend of data packet receiving to the start of ACK packet transmission.14. The Wi-SUN device of claim 1, wherein when the computed immediatechannel access probability is less than the optimal probabilityp_(o)=1/N_(g), the Mode-2 CSMA/CA algorithm performs immediate channelaccess without backoff if channel is idle, wherein if channel is busy, arandom backoff is performed and the Mode-2 CSMA/CA algorithm incrementsthe number of backoffs after the random backoff and assesses Wi-Fi HaLowinterference severity again.
 15. A non-transitory computer readablerecoding medium storing thereon computer executable programs including ahybrid carrier-sense multiple access with collision avoidance (CSMA/CA)control program and Wi-SUN CSMA/CA control program for coexistence of aWi-Fi HaLow network and a Wi-SUN network sharing frequency spectrabetween the networks, wherein the executable programs cause a processorto perform steps of: estimating a severity of Wi-Fi Halow interferencebased on a severity estimation metric; selecting a CSMA/CA mode betweenpredetermined CSMA/CA modes in response to the estimated severity,wherein the switching selects Mode-1 when the estimated severity is anon-severe state, wherein the switching selects Mode-2 when theestimated severity is a severe state, wherein the instructions furtherinclude computing, when Mode-2 is selected, an optimal immediate channelaccess probability based on a number of the neighboring Wi-SUN devicesmonitored by the computing Wi-SUN device; performing an immediatechannel access or a backoff procedure according to the selected CSMA/CAmode; and detecting a channel status based on the hybrid carrier-sensemultiple access, wherein if the channel status is not idle, a maximumallowed number of times for re-attempting a packet transmission ischecked to determine an allowability of re-attempting the packettransmission, wherein when a number of backoffs is less than the maximumallowed number of times, the number of backoffs is incremented.
 16. Thenon-transitory computer readable recoding medium of claim 15, whereinthe severity estimation method estimates the severity based on at leastone of the severity estimation metrics, a channel access failure ratecaused by Wi-Fi HaLow, a channel occupancy probability by Wi-Fi HaLowand a collision probability caused by Wi-Fi HaLow.
 17. Thenon-transitory computer readable recoding medium of claim 15, whereinthe predetermined CSMA/CA modes are Mode-1 and Mode-2, wherein Mode-1 isa standard Wi-SUN CSMA/CA procedure and Mode-2 is an immediate channelaccess enabled CSMA/CA procedure.
 18. The non-transitory computerreadable recording medium of claim 15, wherein when the computedimmediate channel access probability is less than the optimalprobability p_(o)=1/N_(g), the Mode-2 CSMA/CA algorithm performsimmediate channel access without backoff if channel is idle, wherein ifchannel is busy, a random backoff is performed and the Mode-2 CSMA/CAalgorithm increments the number of backoffs after the random backoff andassesses Wi-Fi HaLow interference severity again.
 19. A wireless smartutility network (Wi-SUN) device participating in a Wi-SUN network forcoexistence with a Wi-Fi HaLow network sharing frequency spectra betweenthe networks, comprising: a receiver to receive packets of neighborWi-SUN devices; a memory configured to store computer-executableprograms including a hybrid carrier-sense multiple access with collisionavoidance (CSMA/CA) control program and Wi-SUN backoff control program;a processor configured to execute the hybrid CSMA/CA control programincluding instructions that cause the processor to perform steps of:estimating a severity of Wi-Fi Halow interference based on one orcombination of severity metrics; selecting a CSMA/CA mode betweenpredetermined CSMA/CA modes in response to the estimated severity,wherein the predetermined CSMA/CA modes are Mode-1 and Mode-2, whereinMode-1 is a standard Wi-SUN CSMA/CA procedure and Mode-2 is an immediatechannel access enabled CSMA/CA procedure, wherein backoff parametervalues of Mode-2 CSMA/CA are different from default backoff parametervalues of Mode-1 CSMA/CA; computing an optimal probability forperforming an immediate channel access or a backoff procedure accordingto the selected CSMA/CA mode; detecting a channel status based on thehybrid carrier-sense multiple access, wherein if the channel status isnot idle, a maximum allowed number of times for re-attempting a packettransmission is checked to determine an allowability of re-attemptingthe packet transmission, wherein when a number of backoffs is less thanthe maximum allowed number of times, the number of backoffs isincremented; and a transmitter to transmit packets according to adetermination result of the allowability.
 20. A non-transitory computerreadable recoding medium storing thereon computer executable programsincluding a hybrid carrier-sense multiple access with collisionavoidance (CSMA/CA) control program and Wi-SUN CSMA/CA control programfor coexistence of a Wi-Fi HaLow network and a Wi-SUN network sharingfrequency spectra between the networks, wherein the executable programscause a processor to perform steps of: estimating a severity of Wi-FiHalow interference based on a severity estimation metric; selecting aCSMA/CA mode between predetermined CSMA/CA modes in response to theestimated severity, wherein the predetermined CSMA/CA modes are Mode-1and Mode-2, wherein Mode-1 is a standard Wi-SUN CSMA/CA procedure andMode-2 is an immediate channel access enabled CSMA/CA procedure, whereinbackoff parameter values of Mode-2 CSMA/CA are different from defaultbackoff parameter values of Mode-1 CSMA/CA; performing an immediatechannel access or a backoff procedure according to the selected CSMA/CAmode; and detecting a channel status based on the hybrid carrier-sensemultiple access, wherein if the channel status is not idle, a maximumallowed number of times for re-attempting a packet transmission ischecked to determine an allowability of re-attempting the packettransmission, wherein when a number of backoffs is less than the maximumallowed number of times, the number of backoffs is incremented.